For a long time, coal has occupied a dominant position in China 's energy production and consumption structure. How to realize the clean and efficient utilization of coal has become a research hotspot. As a special oil and gas resource with abundant reserves, tar-rich coal can be converted into gas and liquid fuel by in-situ pyrolysis, so as to realize clean and efficient utilization. However, the temperature variation characteristics of overlying strata during pyrolysis are the key factors that determine the stability of rock strata and underground environmental pollution. It is of great significance to study its variation law for underground environmental protection and pollution prevention. This study focuses on the practical problems in the exploitation and utilization of tar-rich coal in northern Shaanxi.According to the stratigraphic structure and lithology data of the study area, a self-designed and processed similar simulation device for in-situ pyrolysis of tar-rich coal was used to build an in-situ pyrolysis test model of tar-rich coal based on similarity theory. The temperature variation law and its influencing factors of in-situ pyrolysis overburden of tar-rich coal were studied, and the temperature numerical model was further constructed to predict the influence range of different pyrolysis temperatures on overburden. The main research results are as follows:
(1) The temperature of overlying rock shows an upward trend at different pyrolysis temperatures. The closer to the heat source, the faster the rate of increase and the greater the temperature change. The rock layer within 8 cm from the heat source rises rapidly in the early stage, and the heating rate decreases after the coal seam begins to pyrolysis, and the temperature tends to be stable after the pyrolysis is completed. The rock mass temperature above 8cm slowly rises to a constant with the pyrolysis of coal seam. During the cooling process, the cooling rate of coal seam and mudstone layer is significantly higher than that of long-distance rock layer, and with the increase of pyrolysis temperature, the time required for cooling increases, and the cooling time is 3-5 times of the heating time.
(2) The similar simulation results show that the longitudinal temperature of coal seam and overburden rock decreases gradually. The temperature of overlying strata within 3cm of coal seam roof changes the most, the temperature of this layer exceeds 300°C, the temperature of overlying strata within 3-6cm exceeds 200°C, and the temperature of overlying strata above 16cm is less than 100°C.
(3) The temperature change is mainly affected by the pyrolysis temperature and heating time. The higher the pyrolysis temperature, the faster the temperature rise of each layer, and the maximum temperature increases. When the pyrolysis heating rate is 5°C/min, the maximum temperature of the coal seam under the four groups of experiments at 500-650°C is 448.9°C, 482.4°C, 531.4°C and 586.3°C, respectively. The temperature of the mudstone layer is most affected by the pyrolysis temperature, from 600°C to 650°C, the temperature increases by 77.3°C. The rock temperature within 2-13.5 cm increases with the increase of heating time. When the pyrolysis temperature and time are increased at the same time, the affected rock layer range is also increased. When the pyrolysis temperature is 650°C, the temperature influence range is the largest, reaching 20 cm.
(4) The numerical simulation results show that the range of temperature longitudinal diffusion increases by 2 m for every 50°C increase in pyrolysis temperature. The temperature transfer range increased from 40 m to 46 m after pyrolysis at 500°C and 650°C for 10 h, respectively.
谷歌
火狐
